AS Science In Society 1.8
Teacher Notes
Introduction
This question looks at the evidence for genetic risk factors for a major cause of blindness and then at the
influence of two lifestyle factors and how these might interact with the genetic risk factors. Finally
students have to translate the information into a health education message.
Suggested answers
 one allele increases risk
 two increases risk (by approximately same amount) again
 gene 2 has greater effect than gene 1
 very strong effect/ each allele doubles risk
 2 CF alleles leads to certain illness
 AMD alleles increase risk /not certain
 CF/ sickle cell are recessive one allele has no effect
 group studied prospectively
 monitored for risk factors
 outcomes compared for groups with and without risk factors
 5.66 x 6 = 34
 risk is 34 per 1000
give 2 marks for correct answer
 true value not known
 true value lies somewhere between 3.69-8.76
 this is known with 95% probability
 wide confidence interval means a lot of uncertainty over true
value
any 3 for 1
mark each
3
any 2 for 1
mark each
2
any 2 for 1
mark each
2
for 1 mark
each
2
any 2 for 1
mark each
2
(c)(i)



any 2 for 1
mark each
2
(ii)



any 2 for 1
mark each
2
(d)
use level guidance below to put answer into one of 3 levels
Points that might be included, credit any other valid ones
 what is AMD
AMD families
 at greater risk/ inherited risk
 not certain to develop AMD
 risk can be reduced by lifestyle choices
 specific advice on lifestyle
general public
 risk figure
 lifestyle choices increase/double risk
 specific advice on lifestyle
(a)(i)
(ii)
(iii)
(b)(i)
(ii)
Page 1
obesity and smoking increase risk of AMD
increases risk for those with normal and high risk alleles
an example of risk increase e.g. from 1.00 to 1.98 for
obesity in YY
both increase risk
neither causes directly
effect is additive /lifestyle factors have greater effect if risk
alleles also present
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.8
Level
Descriptor
3
Good
Claims supported by an appropriate range of
evidence
Good use of information or ideas about science going
beyond those given in the question
Argument well structured with minimal repetition or
irrelevant points
Accurate and clear expression of ideas with only
minor errors of grammar, punctuation and spelling
2
1
0
Teacher Notes
Mark
range
5-6
Level guidance for
this question
two points from each
section well done
Use structure/
appropriate language
for 5/6
Must be aimed at
public for 6
Modest
Claims partially supported by evidence
Good use of information or ideas about science given
in the question but limited beyond this
The argument shows some attempt at structure
The ideas are expressed with reasonable clarity but
with a few errors of grammar, punctuation or spelling
3-4
Limited
Valid points but not clearly linked to an argument
structure
Limited use of new information or ideas about
science
Unstructured
Errors in grammar, punctuation and spelling or lack of
fluency
1-2
Incorrect or no response
0
any 3 points
Use quality of
explanation structure/
language for 3/4
only 1 or 2 points
Quality of explanation
and language for 1/2
Data taken from D.A.Schaumberg et al (2007) A prospective Study of 2 Major Age-Related Macular Degeneration
Susceptibility Alleles and Interactions With Modifiable Risk Factors Arch Ophthalmology. 2007;125:55-62
October 2008
Page 2
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.8
Student sheets
Age-related macular degeneration, AMD, is one of the most common causes of blindness or poor vision
in older people. There is some evidence that the causes are genetic and two genes have been identified
as increasing the risk of AMD. The data in this question are all taken from an ongoing cohort study of a
large number of health workers in the USA.
risk gene
1
2
allele
YY (normal)
YH
HH
AA (normal)
AS
SS
Incidence rate of AMD in those with risk
allele as a ratio of rate in those with normal
gene (IRR)
(95% confidence interval)
1.00
1.98 (1.64 – 2.40)
3.92 (2.69 – 5.76)
1.00
2.38 (1.92 – 2.96)
5.66 (3.69-8.76)
Figure 1 Risk of developing AMD associated with two particular genes
(a) (i) What does the information in figure 1 tell you about the effect of these alleles on the risk of
developing AMD?
..................................................................................................................
..................................................................................................................
..................................................................................................................
..................................................................................................................
(3 marks)
(ii) How is this different from the effect of an allele such that for cystic fibrosis or sickle cell disease?
..................................................................................................................
..................................................................................................................
(2 marks)
(iii) What is meant by a cohort study?
...............................................................................................................................
...............................................................................................................................
(2 marks)
Page 1
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.8
Student sheets
(b) (i) If the incidence of AMD in the normal population of this age group is
6 per 1000 then what is the incidence in those with SS alleles on gene 2?
..................................................................................................................
..................................................................................................................
(2 marks)
(ii) What is the meaning of the ‘95% confidence interval’ shown in brackets for the SS alleles as 5.66
(3.69 –8.76)
..................................................................................................................
..................................................................................................................
(2 marks)
Risk factor
Alleles
YY
HH
BMI* <30
IRR
1.00
3.96
BMI >30
IRR
1.98
12.28
non-smoker
IRR
1.00
4.23
smoker
IRR
2.34
8.69
*BMI stands for Body Mass Index. High values are an indication of obesity
Figure 2 Risk of developing AMD according to two genotypes and two lifestyle risk factors
(c) (i) What does the information in Figure 2 tell you about the affect of the lifestyle factors of obesity and
smoking on the risk of developing AMD?
..................................................................................................................
..................................................................................................................
..................................................................................................................
(2 marks)
(ii) What would you say if you were asked, “Is AMD caused by genes or by lifestyle?”
..................................................................................................................
..................................................................................................................
..................................................................................................................
..................................................................................................................
(2 marks)
Page 2
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges
AS Science In Society 1.8
Student sheets
(d) Write a short information leaflet, based on research reported here, suitable for use in an optician’s
waiting room entitled;
How to reduce your risk of developing age-related macular degeneration
Include information for those who know AMD runs in their family as well as for the general public.
(6 marks)
Total 21 marks
Page 3
©The Nuffield Foundation, 2008
Copies may be made for UK in schools and colleges